This application claims priority under 35 U.S.C. Sec.119 to a patent application No.2001-32865 filed in Japan on Feb. 8, 2001, the entire content of which is herein incorporated by reference.
1. Field of the Invention
The present invention relates to a helical compression spring for use in a strut type vehicle suspension, and relates to a strut type vehicle suspension having a helical compression spring.
2. Description of the Related Arts
In general, a vehicle suspension is provided with a helical compression spring, which is generally designed to provide a coil axis that coincides with a direction of reaction force of the spring. Various types of vehicle suspension system have been known heretofore. Among them, a strut type suspension with a shock absorber employed as a strut for positioning a wheel is popular. According to the strut type suspension, however, due to a displacement between its load input axis and strut axis, a bending moment is exerted on the strut, with side force acting on a guide and a piston of the strut. This side force prevents the piston from sliding smoothly in the guide to act as the shock absorber. In order to compensate the bending moment, it has been known to arrange a coil axis of a cylindrical helical compression spring to be offset to the strut axis.
Since the arrangement between the coil axis of the helical compression spring and the strut axis of the shock absorber is determined geometrically, it has been required that the helical compression spring should be designed to coincide its coil axis with the direction of reaction force of the spring. In order to meet such requirement, various studies have been made, including the article xe2x80x9cApproaches to Minimizing Side Force of Helical Coil Springs in Suspension Designxe2x80x9d, presented by engineers including the inventor of the present application, and received by Japan Society for Spring Research on Aug. 28, 1995, wherein it was proposed to minimize the side force of the helical compression spring.
In contrast, on pages 56 and 57 of xe2x80x9cAutomotive Engineeringxe2x80x9d issued on September 1997, there are disclosed two kinds of spring having a coil axis inclined to an axis of a shock absorber so as to minimize a friction of the shock absorber for a strut type suspension. One spring is so constituted that one end coil is formed into a pig tail coil, and an axis for connecting the center of the pig tail coil and the center of the other end coil is served as the axis of the shock absorber, and that the axis and a spring force direction (reaction force direction) are arranged to provide a certain angle so that they are intersected at the center of the other end coil. The other spring is so constituted that both end coils are formed into the pig tail coils, and an axis for connecting the centers of those end coils is served as the axis of the shock absorber, and that the axis and the spring force direction are arranged to provide a certain angle so that they are intersected at a longitudinal center of the spring.
With respect to the vehicle suspension, further reduction in size is required now. By means of mere improvement made to a supporting mechanism of the strut having a conventional cylindrical helical compression spring, therefore, it is difficult to compensate the bending moment exerted on the strut due to load from a road. Rather, it is necessary to positively increase a side force applied by the helical compression spring to the strut type suspension, especially widthwise of the vehicle. However, it is not easy to apply a desired side force to the suspension by the conventional helical compression spring. By means of the helical spring disclosed in the aforementioned publication of the Automotive Engineering, sufficient side force necessary for the strut type suspension can not be obtained. Namely, it is impossible to apply the side force to the guide portion and piston portion of the strut enough to compensate the side force exerted thereon.
Therefore, the applicant proposed a helical compression spring for a strut type suspension with a simple structure to apply a desired side force to the strut when mounted on the strut type suspension, in a Japanese patent application No. 11-140649 filed on May 20, 1999, which was published under Japanese Patent Publication No. 2000-104772 on Apr. 11, 2000 in Japan. This Japanese patent application corresponds to the U.S. Pat. No. 6,328,290 B1 issued on Dec. 11, 2001 and its divisional patent application which is now pending. According to the helical compression spring as proposed above, by simply installing the helical compression spring as described hereinafter in the suspension without making a specific change to the prior suspension, the spring is properly mounted on the strut so that a reaction force axis of the spring lies approximately on the center of an upper seat, and that the desired side force is applied to the strut, whereby a smooth absorbing operation can be ensured. In the helical compression spring for the vehicle suspension to be compressed between an upper seat and a lower seat, the spring is formed to provide a coil axis that is substantially curved at a predetermined radius of curvature in an unloaded state of the spring, and a pitch of the lower end coil is set to tilt a lower end plane of the spring seated on the lower seat at a predetermined angle to the lower seat in the direction for shortening the longitudinal length of the spring at the inside of the curvature, in an unloaded state of the spring, and/or a pitch of the upper end coil is set to tilt an upper end plane of the spring seated on the upper seat, at a predetermined angle in the direction for shortening the longitudinal length of the spring at the outside of the curvature, in the unloaded state of the spring.
According to the helical compression spring as constituted above, if a position of coiling end of a lower end coil can not be changed, for example, it will be necessary to limit the total number of coils (turns) to 4.55 coils, for example, so as to direct the side force in a predetermined direction. This limitation of the number of coils requires a change of the total number of coils by a unit of one coil. As a result, change in diameter of a coil wire will be necessitated, so that it will be difficult to reduce a total weight of the spring, as explained with referenced to FIGS. 9, 10 and 11, hereinafter.
FIG. 9 shows a model helical compression spring 5x having an end coil center line for connecting the centers of the lower end coil and upper end coil, which coincides with a coil axis of a body portion of the spring, on the z-axis as shown in FIG. 9. In general, the reaction force, which is caused when the helical compression spring is compressed, does not coincide with the coil axis. As shown in FIG. 9, its component projected on the x-y plane is called as a side force (SF), and an angle (xcex8) rotated clockwise from the y-axis indicative of its direction is called as a side force direction. The value and direction of the side force are varied periodically in response to the total number of coils of the helical compression spring, as shown in FIG. 10 and FIG. 11, respectively.
Accordingly, when the helical compression spring as proposed in the above-described Japanese patent application No.11-140649 is installed in the vehicle, it is desirable to adjust the side force not only widthwise of the vehicle, but also lengthwise of the vehicle. In this case, however, different countermeasures will have to be made, in the case where it is possible to change a position of a coiling end of a lower end coil (or upper end coil), or it is possible to change a design of the lower end coil (or upper end coil), and the case where it is impossible to change the position of the coiling end of the lower end coil (or upper end coil), or it is impossible to change the design of the lower end coil (or upper end coil), as explained hereinafter.
In the case where it is possible to change the position of the coiling end of the lower end coil (or upper end coil), the position of the coiling end may be changed to direct the side force in the desired direction. On the contrary, in the case where it is impossible to change the position of the coiling end, the limitation of the number of coils may be made to direct the side force in the desired direction. For example, supposing that the positive direction on the y-axis corresponds to the outside of the vehicle, in order to direct the side force to the outside of the vehicle, the total number of coils may be set to approximately 4.55 coils, whereby the angle xcex8 is zero, as shown in FIG. 11. In the latter case, however, when the spring constant is to be changed, it is necessary to change the total number of coils and the diameter of coil wire by a unit of one coil. Therefore, it will be difficult to meet the requirement for reduction in size. Namely, because the direction of the side force is varied periodically by a unit of one coil, the total number of coils of 3.55 coils or 5.55 coils, for example, other than 4.55 coils, has to be selected.
According to a general procedure of designing a spring, after the diameter of the coil wire was determined so as to provide design stress of an allowable value, the number of coils is determined so as to provide the spring constant of a predetermined value. In this case, however, if the total number of coils is limited, the spring having the total number of coils more than the one designed according to the general procedure as described above will have to be selected. This is because, in the case where the total number of coils designed according to the general procedure was 4.7 coils, for example, if the total number of coils less than 3.55 coils is selected, the diameter of coil wire has to be made small enough to keep the spring constant, whereby the design stress will exceed the allowable value. In this case, therefore, 5.55 coils has to be selected for the number of coils, and the diameter of coil wire has to be made large enough to keep the spring constant. As a result, the weight will be increased, and the requirement for reduction in weight can not be fulfilled.
Accordingly, it is an object of the present invention to provide a helical compression spring with a side force adjusted easily and appropriately, not only widthwise of a vehicle but also lengthwise of the vehicle, when the spring is mounted on a strut type suspension for the vehicle.
Another object of the present invention is to provide a strut type vehicle suspension for adjusting easily and appropriately a side force applied by a helical compression spring to a strut, not only widthwise of a vehicle but also lengthwise of the vehicle.
In accomplishing the above and other objects of the present application, a helical compression spring for a vehicle suspension according to the present invention is compressed between an upper seat and a lower seat. The spring is formed to provide a coil axis to be substantially curved at a predetermined radius of curvature in an unloaded state of the spring. A pitch of a lower end coil of the spring is set to tilt a lower end plane of the spring seated on the lower seat at a first predetermined angle to the lower seat in a direction for shortening the longitudinal length of the spring at the inside of the curvature in the unloaded state of the spring, and/or a pitch of an upper end coil of the spring is set to tilt an upper end plane of the spring seated on the upper seat at a second predetermined angle in a direction for shortening the longitudinal length of the spring at the outside of the curvature in the unloaded state of the spring. And, the pitch of the lower end coil is set to tilt the lower end plane of the spring at a third predetermined angle to the lower seat on a plane including an end coil center line connecting the centers of the upper end coil and the lower end coil perpendicular to a plane including the end coil center line and the curved coil axis, in the unloaded state of the spring, and/or the pitch of the upper end coil is set to tilt the upper end plane of the spring at a fourth predetermined angle to the upper seat on the plane including the end coil center line perpendicular to the plane including the end coil center line and the curved coil axis, in the unloaded state of the spring.
The spring may be formed to provide a coil axis on the plane including the end coil center line perpendicular to the plane including the end coil center line and the curved coil axis, to be curved in a predetermined direction in the unloaded state of the spring.
A strut type vehicle suspension includes a strut mounted at the upper end thereof on a vehicle body for supporting a wheel, a lower seat fixed to the strut, an upper seat mounted on the vehicle body, and a helical compression spring mounted between the lower seat and the upper seat, with the strut enclosed in the spring. The helical spring is preferably formed to provide a coil axis to be substantially curved at a predetermined radius of curvature in an unloaded state of the spring. The lower seat is fixed to the strut to tilt the lower seat at a first predetermined angle in a direction for shortening the longitudinal length of the spring at the outside of the curvature in the unloaded state of the spring, and/or the upper seat is mounted on the vehicle body to tilt the upper seat at a second predetermined angle in a direction for shortening the longitudinal length of the spring at the inside of the curvature in the unloaded state of the spring. The lower seat is fixed to the strut to tilt the lower seat at a third predetermined angle on a plane including an end coil center line connecting the centers of an upper end coil and a lower end coil of the spring perpendicular to a plane including the end coil center line and the curved coil axis, and/or the upper seat is mounted on the vehicle body to tilt the upper seat at a fourth predetermined angle on the plane including the end coil center line perpendicular to the plane including the end coil center line and the curved coil axis. And, the spring is held in such a state that the inside of the curved coil axis is positioned at the inside of the vehicle body.
In the strut type vehicle suspension as described above, the helical spring may be formed to provide a coil axis on the plane including the end coil center line perpendicular to the plane including the end coil center line and the curved coil axis, to be curved in a predetermined direction in the unloaded state of the spring.